Selective early innervation of a subset of epidermal cells in Xenopus may be mediated by chondroitin sulfate proteoglycans.

The epidermis of early Xenopus embryos is innervated by the Rohon-Beard (RB) neurons lying within the spinal cord and by extramedullary (EM) neurons lying outside of the cord. We have examined the innervation patterns of the three epidermal cell types using wholemount preparations of skin double-labelled with the HNK-1 antibody as a marker for neurons and with antibodies to chondroitin sulfate proteoglycan (CSPG). Cells of one of the three epidermal cell types, here termed conical cells, are innervated well before the other two. In wholemounts of embryonic skin incubated with antibodies to chondroitin-6-sulfate (C6S), all epidermal cells except conical cells show CSPG immunoreactivity in their basal lamina. Double-labelling of skin preparations with HNK-1 and anti-C6S confirmed that these conical cells which lack C6S immunoreactivity are the first to be innervated by RB axons. It is proposed that C6S-bearing proteoglycan initially inhibits innervation of cells whose basal lamina contain the proteoglycan, thus favoring innervation of the conical cells which lack it.